Ganglionic nerve fibres in ventral roots

• According to the law of Magendie, the ventral roots channel efferent nerve fibres from the spinal cord to the periphery, while the dorsal roots channel afferent axons from the periphery into the spinal cord. However, as sensory C-fibres have been observed in mammalian ventral roots outside the autonomic outflow, this law has been questioned. On the basis of other observations, though, ganglionic axons have been suggested not to enter the spinal cord via ventral roots. This thesis presents data on the occurrence of C-fibres in simian ventral roots and provides some new aspects on the occurrence, configuration and function of putative ganglionic ventral root axons in the rat.Paper I shows that putative ganglionic C-fibres occur in the primate ventral root L7, which is outside the autonomic outflow. Like in the cat, these axons do not seem to enter the spinal cord via this root. The ventral root SI does also contain C-fibres, but it seems that these fibres are preganglionic autonomic axons. Some putative ganglionic fibres are also present in the lumbosacral spinal pia mater. Hence, these results conform with the law of Magendie. Paper II shows that putative afferent axons in the rat ventral roots L4-S 1 take a longitudinal course, make zig-zag deviations, loop, branch, end blindly or shift to the spinal pia mater. No putative afferent axons enter the spinal cord via ventral roots. These results agree with the law of Magendie. The results of Paper III suggest that sensory and sympathetic ganglionic axons grow into the rat ventral roots L4-L5 and corresponding pia mater during postnatal development. The afferent axons course as decribed in Paper II. The postganglionic sympathetic axons sometimes loop, but most of them enter the pia mater where they usually associate with blood vessels. A few putative sympathetic fibres enter the spinal cord via ventral roots. Some extra postganglionic sympathetic fibres may enter ventral roots during aging. Paper IV shows that putative afferent rat ventral root axons arecapsaicin-resistant and that they fail to evoke plasma protein extravasation in the root and pia mater. In this respect, they differ from similar axons at many other peripheral locations. The results of Paper V show that C-fibres invade the rat ventral root L5 after neonatal, but not adult, sciatic nerve crush. The extra axons do not seem to represent afferents. At least some proportion of these axons seem to represent putative postganglionic sympathetic axons.

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